Radio receiving system



April 25, 1933. J, P BARTON RADIO RECEIVING SYSTEM Filed March 5. 1930 //l I l *dXZSLQJ -4 7 f\- E I I f 7 INVENTOR James P Barron.

Patented Apr. 25, 1933 UNITEDSTATES PATEN' i'orncs f JAMES EAR'ro-N, F SPRINGFIELD, MAssAorIUsET'rs, AssIeNoE'ro wEs'rINGIIonsE ELECTRIC & MANnrAcTUnINecoMrAnY, A oonronnrronor PENNSYLVANIA *nAnIo RECEIVING sYsrEM I V App1ication filed March 5, 1930. Serial No. 433,294. I

My inve'ntion relates to radio receiving systems and it has particular relation to systems of the type wherein a loop-antenna is utilized for both the receptionand the radiationofenergy. r 7 7 Whena loop-antenna is a constituent part of a combined transmitting and receiving system such as, .for example, an end-to-end communication system for railway trains of- 10 the type disclosed in the copending application of H. C. Forbes, Serial No. 267,585, filed April 5, 1928, and assigned to the WV-estinghouse Electric & Manufacturing Company, it is'highly desirable that means shall be ,5 provided for preventing injury to anyone who might happen to come in contact with the loop when signals are being transmitted.

It is also necessary to provide means for preventing the generation of undesirable oscillations in the receiving apparatus when it isyconnected tothe loop and, for this puriposefa neutralizing network analogous to that disclosedin the patent to Rice, 1,334,118, is advantageous. a v

If the Rice circuit is used exactly as disclosed in the patent, however, it necessitates an additional connection between the center of the loop and the cathodes of the thermionic-tubes in the receiving amplifier and 3 greatly complicates the switching apparatus required for changing the system from the receiving to thetransmitting condition.v

It is, accordingly, an object of my invention to provide, in a combined radio trans- V 3 mitting and receiving system wherein a single loop-antenna is utilized forboth the transmission and the reception of signals, means for preventing injury to, anyone who accidentally makes contact with the loop during the transmission of signals.

, Another object of myinvention is to provide, in a system of the type referred to, means for the prevention of undesired oscillations in the signal-receiving apparatus 5 In applying my invention to a railway signaling system, of type disclosed in the aforementioned application of H, Forbes, I provide a rigid loop-antenna one end of whichis permanentlyconnected to ground through the metallic. portions of the engine Q or car upon .whichit is mounted; Inasmuch asthe cathodes of the thermionic (tubes in boththe transmitting and receiving portions of the system are also connected to ground there is .no necessity for disturbing the ground connection-of the loop when shifting from'the transmitting'to the receiving 0on dition. I connect the other terminal of the loop to a single switching device, therefore, whereby the loop can be associated with the transmitter or with the receiver,.at will; 4 When the switching device is *inthe receivingposition'the ungrounded terminal of the loop isconnected, .through'ayariable tuning condenser,v to one terminal of an input inductor included betweenrthe grid and cathode of the first thermionic'tube in thereceivingamplifier. V

Neutra lization against oscillation in the receiving amplifier is provided for 'by connecting a circuit including an inductor and a variable condensenbet-ween'the' plate of the first thermionic tube and the cathode thereof, and by so disposing the said induc- 75 tor with respect to the input inductor of the tube that the; inductive feedback is in the proper sense. I v The novel features that I consider characteristic of my'invention are set-forth with particularity in the appended claimsf The invention itself, however, both'as to 'its organization and its methodof operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

- The single figure of the drawing is a diagrammatic view ofa portion of-a radio sig- 0 high-frequency energy shall be delivered to the loop-antenna, for radiation therefrom,

and that-the receivingiamplifi er may comprise the usual demodulator andaudio-frequency amplifier stages adapted to deliver;

energy to a loud-speaker or device. 4. r

The apparatus shown in the drawing comprises a loop antenna l one end of which is connected to 'groundthrough the metallic portionsand'the runninggear 2 of a railother indicating way-car (not shown) upon 'whichit is mounted. The other endof the loop leads to aswitching device 8 wherebyit may be selectively associated with the: output cir- 'cuit of a thermionic tube 4 in the transmitting portion of thesystem, or, through a tuning condenser 5, with one end of an input inductor 12 connected between the grid and cathode 10f a thermionic tube 7 comprised in the receiving amplifier. V

The cathodes of the thermionic tubes comprised in the transmitting and receiving'portions of the system -may be energized in parallel from a common source 8 and a common source of plate potential 10v may also be used. 'Bysreason of the fact that the transmitting; tubes require very much higher plate voltages-than the receiving tubes it is customary,however, to supply them with potential from a motor g'enerator.

aIn order to prevent the generation of 0scillations in-' the receiving portion of the system, when the loop and the input circuit are tuned to the frequency of thedesired signal, a neutralizing network is provided, the'said network being constituted by a feed-back condenser 11 and .an inductor fi serially connected between the plate of the tube 7 and the cathode thereof. The neutralizing inductor is disposed in inductive relationto the input inductor 12- and the direction of the windings thereof is so chosen that the potentials induced therefrom across the said input inductorare opposite 'in phase to the potentialsvarising therein by reason of feed-back through the plate-grid capacity of the tube.

v The input inductor and the neutralizing inductor may be constituted by a bi-filar winding or they may be the :halves of a continuous winding'having a mid-tap connected to the cathode oft-he tube, it being primarily essential that there shall be a high value of coupling between the said inductors if the system is to remain free I carrier-frequency at which receptionis desired; Inasmuch as the inductance of the loop is, preferably, made equal to the in ductance of the'inputinductor substantially one half of the available signal potential appears across" the inputterminals of'the thermionic tube.

It will be apparent,"from a consideration ofthe foregoing description of in improved signaling system, that dangerous y high potentials are'prevented,-by the ground'connection, from being developed across the loop-antenna during the transmission of signals. This feature is decidedly advantageous in that it prevents injury to the trainmen should they accidentally make contact with the loop when it is energized, I Furthermore, my invention obviates the necessity of providing the loop with a centerconnection,'jsuch as is-nece'ssitatedfif the Rice circuit is employed exactly as it is shown in the patent, and greatly simplifies the'problem ofshiftingthe loop from the transmitting to the} receiving condition.

Although I 'have' shown and described a specific embodiment. of my invention, I am fully aware that many modifications thereof are possible; My invention, therefore, is not to ,be restricted except insofar as is necessitated by theprior art and by the spirit of the appended claims. I claim as my invention: V

1. In ;a signaling system, a thermionic amplifier having a cathode, a control-elecv trode and an anode,'an input inductor connected between the control-electrode and the cathode, a loop antenna oneltermi'nal of which is connected to the cathode and the other terminal ofwhich is connected,

throughja tuning condenser, to the controlelectrode, and a feed-back inductor and a condenser serially connected between said anode and said cathode, said feedback inductor and said input conductor beinginductively coupled inthe sense to oppose the generation of oscillations in said amplifier.

2 In a' signaling system, a'loop-antenna constituted by a single turn, a thermionic receiving amplifier having-a cathode, a control-electrode 'andan anode',l an input inductor connected between said control-electrode and said cathode, a connection including a tuning condenser between one terminal of the loop-antenna and the control-electrode, a connection between the other terminal of the loop-antenna and thecathode, and means connected between the anode and the cathode for preventing the generation of oscillations in said amplifier.

In testimony whereof, I have "hereunto subscribed my name this 20th day' of February 1930'. V

JAMES P. BARTON. 

